1. Field of the Invention
The invention relates to an apparatus for observing and photographing the endothelial layer of the cornea of a subject's eye by projecting illumination light onto the cornea.
2. Description of the Prior Art
Heretofore, there is known a contact type of apparatus for observing and photographing a corneal endothelium. In this type of apparatus, a liquid anesthetic is dropped in the subject's eye before observing and photographing it therewith. The contact type of apparatus includes a cone lens which is in contact with the surface of the cornea. The apparatus, however, has drawbacks in which the cone lens injures the cornea because of the contact of the lens with its surface and much time is consumed for photography because of disinfection of the lens or the like. To remove those drawbacks, a non-contact type of apparatus has been developed in which a slit lamp is provided with an optical attachment for observing the endothelial layer.
The non-contact type of apparatus can generally decide its position relative to the subject's eye in eye estimation. In the non-contact type of apparatus, illumination light emitted by a light source for observation is projected onto the cornea at an angle, reflected light from the cornea is guided to an eyepiece, and an operator observes the endothelial layer through the eyepiece and brings it into focus. A monitor screen can be also employed to take the focus.
By the way, the cornea itself is thin and its endothelium is composed of a single layer of thin flattened cells that lines the innermost of the cornea. Therefore, the endothelial layer thereof must be highly magnified for observation. However, such a high magnification results in a big vibration of its image caused by the continuous slight tremor of the eye. Therefore, the operator requires great skill to observe and photograph the corneal endothelial layer with the conventional non-contact type of apparatus. For example, the operator must timely push a photographing button as soon as the image is brought into focus. Further, since the non-contact type of apparatus is not predetermined to be precisely positioned relative to the eye, the operator must observe the dark field visible through the eyepiece until the image of the corneal endothelium appears or reflected light from the corneal surface is found out beside the image. This conventional apparatus largely depends on operator's experience and strong intuitive feeling.
Further, since the alignment of the optical system of the apparatus with the eye often requires much time, the subject is compelled for a long time to keep the eye open until finishing photographing it, and hence undergoes much pain.